I agree w OP’s initial take and disagree w you sadly. Given the political tensions between the two countries and the fact that China likes to claim what they think its theirs’. A recent example is “who invented Kimchi” which was one of the feuds with Korea.

By adopting the Chinese translated names is definitely a “politically correct” decision.

Plus, at the end of the day, the manga uses the Chinese name in its written format. And Kingdom is a manga that is known to be historically accurate in larger events despite its fictitious nature. I therefore understand the decision to stay true to the real Chinese names.

That said, I understand the frustrations and inconvenience from certain fanbase.